Medical syringes comprise a cylindrical barrel and a plunger with a cylindrical base made of resilient material located in sealing relation within the barrel and a needle mounted at the base of and in communication with the barrel.
Originally the barrel was made of glass and the syringe was designed for multiple use with either the needle or the whole syringe being subjected to sterilisation between uses. However, for convenience and in order to minimize cross infection, the syringes most used in medicine now are plastic disposables.
Although relatively cheap and disposable, these syringes can be reused and usually are by drug users amongst whom the spread of Acquired Immune Deficiency Syndrome (AIDS) is on the increase because of the sharing of syringes.
Many prior art syringes have been designed in an attempt to prevent reuse. Some use complicated mechanisms to prevent withdrawal of the plunger; these are difficult to manufacture and greatly increase the cost over the plastic disposable. Others use techniques in which the plunger collapses or the seal between the plunger and the barrel is broken, which prevents suction. None of these have proved to be reliable and affordable and although medically desirable have not been successful.